1. Field of the Invention
This invention relates to negative-working diazo processes, and more particularly, to an improved light-sensitive diazo film capable of being undergoing autocoupling to produce a negative print of an original having good visual properties.
2. Description of the Art
The diazo process is basically a positive printing process in that the non-image areas of an original transmit actinic radiation to the light-sensitive coating, and, in these areas, the diazo compound is decomposed. Thus, its capacity for subsequent coupling to form a dye-image is destroyed. This decomposition product usually does not react with further undecomposed parent diazo compound unless the photolysis product is reactive enough. However, under favorable conditions, it can react with non-decomposed diazo compound to form a dye in the partly exposed areas, but not in the areas protected from light. Thus a negative print of the original results.
Such a negative printing process ideally should involve a 50% decomposition of the diazo compound followed by autocoupling between the remaining half of the parent diazo compound with its decomposition product to form the desired dye-image. This autocoupling reaction can be initiated as in positive systems by increasing the pH of the substrate with a weak solution of ammonia, gaseous ammonia, or other bases. The remaining diazo if present, can be removed by a second exposure step.
The negative diazo process has not been very successful, however, because the ratio of the photolysis product to the residual diazo is difficult to control, with the result that the density of the dye-image is lower than that which is required for a commercial system.
Accordingly, it is an object of the present invention to provide a new and improved negative-working diazo printing process.
Another object of this invention is to provide a negative process which is capable of providing prints having relatively high image densities.
A further object of this invention is to provide a light-sensitive diazo material for a negative-working diazo process which is capable of undergoing autocoupling to produce a dye-image having good visual properties and high actinic density.
These and other objects of the invention are achieved herein by the provision of a negative working diazo process in which the light-sensitive layer of the diazo paper is a diazo oxide having a chemical additive therefor which significantly enhances the image density of the image dye produced in the process.